Dehydrohalogenation of alpha-chloroisobutyric esters with zinc and zinc halides



e nati n Of an p yd c b n ph -ha owise as the reaction proceeds. The crude distil-v Wcllid have been expected to take Place as lation under reduced pressure. The distillate v uNIranenres PATENT QFFICE i izh eam DEHY DR OHALO GENATI ONI F ALPHA-dimo- 3 ROISOBUTYRIC ESTERS WITHZING ZINCHALIDES W Harold J. Barrett, Niagara Falls, Y., assignor I to E. I. du Pont de Nemourskit Company, 'Wilmlngton, Del., a corporation of'Delaware NdDrawing; Application-April 3, 1937, Serial No 13;,741) I '10 Claims. (Cl.'2 60---46) This invention relates to a process for the pro- The invention will be further illustrated by the duction of alpha beta-unsaturated acid'esters. following examples which will not in any way. More particularly it relates to a process forthe limitthe scope ofthe invention to specific proproduction of methacrylic acid esters by treatportions or reactants therein given:

ment of alpha-halogenated isobutyric acid esters 5 with zinc. v 7 Example} An object of this invention is to provide a pro- A .mixture of 500 grams of methyl alphacess for the preparation of alpha-substituted chloroisobutyrate and 26.6 grams of zinc powder acrylic acid esters by anew and economical was heated under a distilling column with a re-' P A fu e bj ct of he inventi n is t flux adjusted so that the distillate consisted 10 provide a process for the preparation of alpha largely of methyl methacrylate along with hydrobeta-unsaturated acid esters by the dehydrohalogen chloride. The zinc may be added portiongenated propionic acid ester. Oth bje ts a late was Washed with aqueous sodium carbonate advantages of the invention will hereinafter (to remove acid), dried, and distilled (with th 1!! appear. addition of 2.5 grams of hydroquihone to prevent These and other o je s are cc mpl shed by polymerization). A 220 cc. portion of methyl heating n ester f n phayd b n a1 ,hamethacrylate was obtained boiling at 98-101 0. halogenated propionic acid with zinc an irae-v The higher boiling portion of the distillate is tionating the reaction product to isolate. the largely unreacted met yl alpha-chloroisobutyalpha beta-unsaturated acid ester or esters and rate, i 1 I v cov unchanged, p yd iph -.The above example indicates that the reaction alogenated Dropichic acid ester- .7 is catalytic in nature rather than a double de- Aecording t0 e invention an ester s chher composition reaction, since 0.42 atom'of zinchas xamp e, e methyl es of h h e led to'the'production of more than 2 mols' or butyric acid is heated with zinc under a distilling et methacrylate, s au proportions of l mn with a reflux so adjusted ha he m t zinc will suffice in this reaction and when much me y e, along With hydrochloric acid, largerproportions of zinc are used, as in the removed from the r i n mix f m following examples, the reaction proceeds in a while the unreacted chlorester i returned to h similar manner with most of the zinc recoverable no reaction vesse T resulting distillate s in an unaltered condition at the end of the retreated with an alkaline substance such, for exaction, I p r ample, as the alkali metal or alkaline earth metal hydroxide or carbonate, to remove free hydro-r chloric aci dried, and fractionated to, separate A mixture of 100 grams of granular zinc and the methyl methacrylategirom any unchanged -i6o-;grams p1;-ethyl,,alpha chloroisobutyratewas chloroisobutyric ester that may have distilled heated under a distilling column withthe reflux over in the initial fractionation. adjusted so that the distillation temperature n the Present invention Zinc appears to act never exceeded 128 C. Most of the zinc was ceteiytieelly, causing the removal of e m of unaltered at the end of the reaction. The distil- 40 hydrogen ha ide p r m i f ester, rather than, late was washed with sodiumv carbonate, dried as would be exp n e i g i o he reac on over calcium chloride, and fractionated, yielding with the formation of zinc c loride. The reac- 32 grams of ethyl methacrymta tion follows the equation:

I Zn Example II CHFCX-COOR 0H,=o-ooon+HX A mixture of 450 grams of butyl alpha- Ha Ha chloroisobutyrate, 250 grams of zinc dust, and

- gram of hydroquinone was heated until the inin which R is an alkyl group and X haiogfanitial vigorous reaction subsided and the liquid This is a Surprising result Since the E P was removed from the reaction vessel by distil- Ewampie II cated in the equation below: was washed with sodium carbonate, dried, and R fractionated at atmosp eric pressure. Butyl 2RX+ZIH R+ZHX2 methacrylate obtained amounted to 250 grams.

in which R is an alkyl group and X a halogen. In Examples 11 and I1I',a small amount of hyolymerization inalpha-chloropropiomc acid, alpha-phenyl alphachloropropionic acid, etc.

1. A-process for the preparation of esters of alpha beta-unsaturated acids dehydrohalogenating,

eifect dehydrohalogenation, an alpha-hydroalpha-halogenated propionic ester in the presence of a substance selected from the group consisting of zinc and zinc halides as the catalyst, substantially in accord with the equation:

X Zn CH3-C-C00R oH,=o-oooR+Hx 2. The process of claim 1 in which the halogenated ester is an alpha-alkyl substituted alphachlorinated propionic acid process for the preparation of methyl methacrylate which comprises heating to refluxchloride, at a temperature sulficient to elfect deation.

and 0., distilling olT the methacrylate together with the hydrogen chloride, washing and neutralizing the crude distillate and subsequently drying and purif tillation the neutralized product, in

polymerization inhibitor.

HAROLD J. BARRETT.

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